Photographic reducer



Jan. 7, 1941.

G. P. HAM 2,227,644

PHOTOGRAPHIC BEDUCER Filed Dec. l2, 19159 ore/@M142 parra? 5 ,4f-nn? /5 Arf-fl? 35' grrr/P 65 BY Y/ I l ATTORNEY.

INVENTOR.

Patented Jan. 7, 1941 UNITED STATES PATENT OFFICE PHOTOGRAPHIC REDUCER Application December 12, 1939, Serial No. 308,775

2 Claims.

This invention relates to new and improved reducing compositions for photographic material.

A number of reducing compositions have been developed to reduce the density of photographic 5 material. These reducing compositions are of various types but in general may be classified into three main categories. First, cutting reducers, that is to say, reducers which take nearly or as much silver off the portions of the photographic material which have small amounts of silver corresponding to shadows in a negative or high lights in a positive, and hence result in an increase in contrast because the denser portions are not decreased proportionately as much.

'Iypical of these reducing compositions are those employing ferricyanides. The second type is the so-called proportional reducers such as those using persulfates in which dense and light deposits are reduced proportionally and no change in contrastis eiected. Finally, the third category is the superproportional reducers in which the denser portions are reduced more than in proportion to the lighter deposits.

'I'he present invention deals with compositions of the iirst category, that is to say, cutting reducers. In the past potassium ferricyanide has been used as the reducer, being referred to frequently as Farmers solution, and a. typical reducer of/this type is represented by Eastmans fir-4A. y/f/ The eiiiciency of a cutting reducer depends on two factors, one is the speed with which a given ldegree of reduction is eiected, andthe other, and more important, is the amount of contrast which is obtained. It is particularly important to be able to cut correctly without too great a change in contrast. This is particularly imlportant when it is desired only to cut the very lightest deposits, as for example, when an overexposed or over-developed negative shows a fog. It is desired to cut out the fog' without affecting the fidelity of the remaining image, and this should be effected as fast as possible because ferricyanide reducers have a softening action on the photographic emulsion and should be in contact for as short a period of time as is con- V sistent with satisfactory cutting or reduction. Tripotassium ferricyanide has been/ the standard reagent in the Farmers reducing solution and it was believed that Ithe action was due entirely to the ferricyanide and the cation was of no importance.

'Ihe present invention is based upon the [dis-l covery that the cation is not' without .significance i and particularly that important results can-bc 'obtained when monosodium dipotassium ferricyanide is used in place of the tripotassium ferricyanide. The present invention produces a reducing composition which can be handled in exactly the same fway as the standard potassium ferricyanide reducers but possesses advantages in that the cutting of the very lightest silver deposits takes place with extreme rapidity and the resulting image retains good fidelity. The monosodium dipotassium ferricyanide reducer of the 10 present invention differs from tripotassium showing a materially more rapid reducing action Without loss of deiity. n

The present invention is not directed to any difference inprocedure except the difference in 15 the ferricyanide used and this is -an advantage `because the 'photographic technician is not required to modify his standard technique or procedure.

'I'he results obtainable by the present invention 20 are illustrated in the drawing in which:

Fig. 1 is a series of curves obtained by a reducing solutionv containing tripotassium ferricyanide; and c f Fig. 2 is a similar set of curves obtained by -a 25 solution using a corresponding quantity of monosodium dipota-ssium ferricyanide.

The invention will be described in detail in the following specific example, it being understood that the invention is not limited to the exact pro- 30- portions therein set forth, but is applicable to any other formula of ferricyanide reducer.

i A photographic wedge with logarithmic steps representing a 50% increase in exposure from step to step, was contact printed onto a series 35 of 35 mm. super sensitive p anchromatic lm, using an Aextremely accurately controlled uniform exposure obtained by a beam from a Leitz enlarger 'with the lens stopped down to its smallest opening. The series of strips of film were deo veloped in a single solution of Eastman DK-'50 developer using stagnant development for 10 minut at 18 C. They were then fixed with a standard Eastman F`5 fixer without using any special gelatin hardening solution other than the 45 alum in the fixer. One of the strips was measured on a densitometer and the other strips Were'put in a reducer solution prepared as follows:

A solution of 8.60 grams of sodium dipotassium ferricyanide and cc. of water was prepared, 50 together with a second solution of 60 grams of sodium thiosulfate crystals in 250 cc. of Water.

\30 cc. of the first solution and 120 cc. of the second wereinixed together and 850 cc. of water added. The strips were then passed in this mix- 55 ture and the temperature maintained belowr 24 C. At the end of rive minutes, one vof the strips was removed and washed, a second after 15 minutes,

a third after 45 minutes and a fourth after 60 minutes. The reduced strips after drying were all read on the same densitometer and the densitometric curves are shown in Fig.- 2 of the drawmg.

A similar procedure was followed with a further number of strips by using 7.5 grams of tripotassium erricyanide instead of 8.6 grams of monosodium dipotassium ferricyanide. All of the strips were read on the densitometer as before, and the densitometric curves appear in Fig. 1 of the drawing.

It will be noted that in both cases sharp cutting was noted even after ve minutes. The degree of cutting in the denser parts was somewhat greater, but in the lighter deposits, whereas only the rst wedge strip in Fig. 1 had been re--l` duced to the minimum density determinedby the inherent color of the clear gelatin, the second wedge strip had disappeared in Fig. 2. That is to say, while the potassium ferricyanide had only cut one wedge step, the sodium dipotassium ferricyanide had cut two. At fteen minutes and after, the behavior of reduction was substantial- 1y the same except thatl reduction could be continued for a longer time with the sodium dipotasanemia sium ferricyanide without losing fidelity. II'he rapid cutting of the smallest silver deposits with short exposure to the reducer which is noticeablev with sodium dipotassium ferricyanide represents an important advantage because even with a very short treatment which will not seriously injure the gelatin, it is possible to cut fog and other veiling deposits which is the primary unctionbf a cutting reducer. At the same time this is obtained without loss of fidelity, nor is there any staining of the gelatin. Y

What I claim is: Y

` 1. A method of reducing developed silver halide e 

